This invention relates to the art of blow molding from a parison of particles of organic plastic material susceptible to the improvement of their properties by orientation and has for its principal objects the improved adjustment of the temperature of the parison, carrying out the steps of parison production, stretch orientation and circumferential orientation in a single uninterrupted, yet completely controlled sequence, and the provision of improved, oriented hollow articles and a method and apparatus for obtaining same.
The art teaches various methods and apparatus for obtaining blow molded articles of organic plastic material from a parison, such as in U.S. Pat. No. 3,349,155 and Re. U.S. Pat. No. 27,104. Generally these methods are characterized by forming a parison in a parison mold on a blow core, placing said formed parison and blow core into a blow mold and expanding said parison in the blow mold by means of fluid pressure.
While the blow molding operation tends to impart orientation to the article, such orientation is predominantly circumferential, i.e., not bi-axial. Also, the degree of such orientation is difficult to control. It is therefore difficult to obtain the advantageous properties in the article that bi-axial orientation is capable of providing.
It is known that the control of orientation depends largely upon the control of the temperature of the parison just prior to orientation. It is found that such temperature control is best obtained by enclosing the article prior to the orienting step in heating means that impart temperatures, preferably by contact with the corresponding surfaces of the parison, to the regions of the parison corresponding to the degree of deformation that is intended for such regions.